Earlier quoted context omitted.
Why wouldn't it scale to Wal-mart? Even with a dozen people with the same name in the store, a cashier can quickly pick a matching face: everyone is good at that (except for prosopagnosics). And that's without assuming Wal-mart adds any extra hardware that could narrow the position of handhelds to individual registers.
That's a pretty long scroll box to find the person in the first place. Or an added step as you key in the first few letters of the person's name. At large retailers or QSR chains that put a premium on fast checkout, neither option will fly. I obviously appreciate the simplicity of paying with your face.
The general point of scale issues still is valid, but culling the list of payers seems surmountable.